Manufacturing processes and techniques
What this domain tests
Manufacturing questions ask you to match a process to a scale of production, material and shape, and to explain the trade-off between tooling cost and unit cost.
Scales and processes
- One-off: craft methods; jigs rarely justified; high labour per unit.
- Batch: jigs and moulds spread over a run; flexible enough for variants.
- Mass/continuous: high tooling cost, low unit cost, dedicated lines, quality control by sampling and statistical process control.
- Forming: vacuum forming (thermoplastic sheet over a mould), line bending, injection moulding (granules to heated barrel to screw to mould), extrusion (constant profile), blow moulding (hollow bottles), press forming and forging (metal), casting (pouring liquid into a mould), 3D printing (additive, good for one-offs and complex internal shapes).
- Joining: temporary (screws, bolts, knockdown fittings) versus permanent (adhesives, welding, brazing, rivets, wood joints).
- Jigs and fixtures locate and hold work for repeatable production; a jig guides the tool, a fixture holds the work.
Worked example
Choose a process for 50,000 identical ABS enclosures with 2 mm walls and internal bosses. Injection moulding is selected: the mould costs tens of thousands of euros, but at 50,000 units the tooling is spread thinly and cycle times are seconds. Vacuum forming cannot form internal bosses easily and leaves webbing; 3D printing would take hours per part and has a higher unit cost. Draft angles are added for release and wall thickness is kept uniform to avoid sink marks.
Traps
- Choosing 3D printing for mass production.
- Confusing vacuum forming with injection moulding.
- Ignoring tooling cost when comparing processes.
- Forgetting draft angles, shrinkage or uniform wall thickness in moulded designs.